This invention relates generally to electronic memories and particularly to electronic memories that use phase change material.
Phase change materials may exhibit at least two different states. The states may be called the amorphous and crystalline states. Transitions between these states may be selectively initiated. The states may be distinguished because the amorphous state generally exhibits higher resistivity than the crystalline state. The amorphous state involves a more disordered atomic structure. Generally any phase change material may be utilized. In some embodiments, however, thin-film chalcogenide alloy materials may be particularly suitable.
The phase change may be induced reversibly. Therefore, the memory may change from the amorphous to the crystalline state and may revert back to the amorphous state thereafter, or vice versa, in response to temperature changes. In effect, each memory cell may be thought of as a programmable resistor, which reversibly changes between higher and lower resistance states. The phase change may be induced by resistive heating.
Because of the high potential storage capacity of phase change memories, and for other reasons, it would be desirable to make phase change memories with as many memory storage locations as possible per unit of area. One issue with existing phase change memories is that an isolation diode may be used between the memory cell itself and the word line. The isolation diode is typically a p-n junction diode. The use of a p-n junction may limit the scalability of the overall memory array inter alia because the p-n junction may not be very vertically scaleable.
Thus, there is a need for better ways to isolate phase change memory elements.